The Bluefin 21, the Artemis autonomous underwater vehicle (AUV), is hoisted back on board the Australian Defence Vessel Ocean Shield after a successful buoyancy test.

PETALING JAYA - The oil slick detected by the Australian Defence Vessel Ocean Shield is not from an aircraft, said Joint Agency Coordination Centre (JACC) chief coordinator Angus Houston.

"Preliminary analysis of the sample collected by ADV Ocean Shield has confirmed that it is not aircraft engine oil or hydraulic fluid," said the retired Air Chief Marshal in a statement issued on Thursday on the search for the wreckage of the missing Malaysia Airlines flight MH370.

It also said that Phoenix International, with the assistance of Bluefin, makers of the unmanned submarine, have assessed that there is a small but acceptable level of risk in operating the Blufin-21 in depths in excess of 4,500m.

This expansion of the operating parameters allows the Bluefin-21 to search the sea floor within the predicted limits of the current search area.

The JACC refuted reports stating that it would take the unmanned submarine anywhere from six weeks to two months to scan the underwater search area, saying such reports were "incorrect."

"Since the US Navy provided comment some days ago, the underwater search has been significantly narrowed through detailed acoustic analysis conducted on the four signal detections made by the towed pinger locator on ADV Ocean Shield," said the JACC.

It added that the analysis had allowed the underwater search area to be reduced and focused.

"This represents the best lead we have in relation to missing flight MH370 and where the current underwater search efforts are being pursued to their completion so we can either confirm or discount the area as the final resting place of MH370," said the JACC.

MH370 was missing for 17 days before it was declared by Prime Minister Datuk Seri Najib Abdul Razak on March 24 to have ended its flight in the Southern Indian Ocean.

It had disappeared from Malaysian radars at 2.15am on March 8 after taking off from Kuala Lumpur International Airport for Beijing at 1.30am. It carried 239 passengers and crew.